LEDs have been used in various applications including illuminating watches, transmitting information from remote controls, and forming images on jumbo television screens. More recently, LEDs have been used in portable lighting devices (such as flashlights), because, among other things, LEDs can last longer, produce light more efficiently, and can be more durable than incandescent lamps commonly used in conventional flashlights. Moreover, because flashlights that use incandescent lamps dominate the field, LED modules (a module that uses an LED as its light source) have been designed that can be retrofitted into existing flashlights.
A problem with simply replacing an incandescent lamp of an existing flashlight with an LED module, without more, is that it fails to operate the LED at its potential lighting capacity under a thermally stable condition.
It is known that LEDs produce more light with increased forward current. In situations where available voltage is abundant, the LED may be driven close to its maximum forward current value to produce more light. However, where the available voltage is limited or depletes over time, such as in the case of a battery powered flashlight, delivering a forward current close to the LED's maximum value may not be possible. A similar concern exists if the battery or batteries contained in an existing flashlight provides too much voltage, thereby delivering a forward current above the LED's maximum value, which will result in damage to the LED.
Another problem with simply replacing an incandescent lamp of an existing flashlight with an LED module is that it fails to address the thermal consequences associated with LEDs. Although LEDs produce light more efficiently than their incandescent counterparts, LEDs generate significantly more heat. Therefore, effective dissipation of heat is needed to maintain the LED temperature within its design limits. One effective way of dissipating heat generated by a light source in a flashlight is disclosed in a co-pending application Ser. No. 10/922,714 entitled Improved LED Flashlight, filed Aug. 20, 2004, which is hereby incorporated by reference.
However, in the case of an LED module that is designed for retrofit, the existing flashlight into which the LED module is used may not be able to sufficiently dissipate the increased heat that is produced by the LED. Most LEDs have projected life and lumen capacity that is conditioned on maintaining a prescribed LED operating temperature. If this temperature is not maintained, the life and/or the strength of the light generated by the LED diminishes. Accordingly, if the existing flashlight into which the LED module is retrofitted is insufficient in this regard, the LED module itself must self-control the amount of heat that the LED generates to ensure that the LED or the electronics that may control the LED are not damaged.
Existing LED modules have attempted to address the thermal dissipation problem by limiting the current delivered to the LED to a continuous value at a safe level much below its potential light emitting capacity. However, such an approach makes inefficient use of the LED's lighting capacity and the LED's full lighting potential is never achieved.